Lignin enhanced shape memory polyimide with superior mechanical property and performance

Shape memory polyimide (SMPI) has excellent thermal stability and chemical inertness, and was used in high-end applications, such as aerospace, microelectronics, etc. However, the unsatisfied strength and toughness is currently the key challenges of SMPI. Herein, lignin, a natural polymer, with abundant rigid benzene ring structures and reactive functional groups is used to enhance SMPI’s mechanical properties and shape memory performance. The formation of hydrogen bonds and π-π interactions between lignin and SMPI matrix resulted in the simultaneously enhancement of strength and toughness through in-situ polymerization. As a result, the tensile strength and strain of composite films is increased from 73.45 MPa and 5.2 % to 114.5 MPa and 90.2 % at lignin content of 4 wt%, which are remarkably increased by 156 % and 1734 %, respectively. The shape recovery triggering temperature decreases ∼ 7°C with the increase of lignin content. What’s more, the shape fixation rate ( R f : 99.8 %) and recovery rate ( R r : 100 %) of L/SMPI composite films was also improved, and various complex shapes can be molded. The good thermal stability was well maintained, in which the decomposition temperature ( T d ) is ∼ 507 °C and the glass transition temperature ( T g ) is ∼ 181 °C. The excellent performance of lignin-modified shape memory polyimide (L/SMPI) opened a new ear for high value application of natural polymer, particularly in shape memory material.